1. Field of the Invention
The present invention relates to an infrared detector of the type suitable for use in burglar alarm systems and automatic light switches.
2. Description of the Prior Art
Infrared detectors are generally known in the art which include at least one detector element mounted in a housing which has a window covering the detector element which is transmissive for infrared radiation. The housing also contains further electrical components interconnected with the detector element.
Infrared detectors of this type using pyroelectric detector elements are principally used in burglar alarm systems and automatic light switches. It is known that the temperature of a human body is usually different from the environment. A person moving in the field of view of an infrared detector causes a change in the radiant power incident on the detector element, and thus the temperature of the detector element also changes. This results in a spontaneous polarization of the detector material, due to the pyroelectric effect, resulting in the generation of charge. The charge is acquired at electrodes of the detector, and is shaped into a voltage signal using an impedance converter. A field effect transistor having a low gate leakage current is generally used as the impedance converter.
In conventional infrared detectors of the type described above, the window which is transmissive for infrared radiation is glued in a metallic housing cover. The electrical components and the detector are mounted on a plate in another housing portion, which is then closed by the cover, and the two housing parts are tightly joined to one another.
In conventional infrared detectors, therefore, a disadvantage exists that automatic checking and positioning of the detector element relative to other components of the device can only be undertaken to a limited degree, or only with relatively complicated specialized equipment.